A grating (sometimes termed a diffraction grating) is a light-modulating optical component with a surface covered by a regular pattern of parallel lines, typically with a distance between the lines comparable to the wavelength of light. Gratings are commonly used in spectrum analyzers, diffractometers, spectrometers, and optical beam steering devices for display units. Light rays that pass through such a surface are bent as a result of diffraction, related to the wave properties of light. This diffraction angle depends on the wavelength of the light. Alternatively, the grating may have a regular pattern of fixed mirrors (or other highly reflective surface) such that the reflected light is diffracted as desired. One drawback of such fixed gratings is that their spectral properties cannot be changed (i.e., such gratings are non-dynamic).
Microclectromechanical systems (MEMS) grating devices exist that are able to dynamically control the spectral properties. Such a device consists of a number of aluminium-coated ribbons suspended over a thin air gap. Each ribbon can be pulled down a controlled distance into the air gap by means of an electrostatic charge. When all the ribbons in a pixel are in their rest state, their aluminum coatings act as a mirror, reflecting light away from the projector's optical path. If alternate ribbons in a pixel are pulled down, a square-well diffraction grating is formed in which each well has a depth equal to a fraction of the wavelength of light. Light waves reflecting off adjacent “up” and “down” ribbons are therefore out of phase with each other, different wavelengths by differing amounts. This causes the waves to interact in a way which causes each frequency of light to radiate from the pixel at a different angle. By varying the width, separation and degree of pull-down of the ribbons in each pixel, the spectral properties of the light can be controlled. While such MEMS gratings are dynamic, the speed with which the spectral properties can be changed is limited by the weight, spring constant, and driving forces of the components. Further, having such moving mechanical parts can result in deterioration of the moving parts due to friction and stress.
As such, it would be desirable to have an optical grating device capable of dynamically and rapidly changing the spectral properties of reflected or transmitted light, without moving parts.